The present invention relates to a disk on which map data for guiding an object such as a motor vehicle to its destination are recorded, and to a navigation apparatus using such a disk.
FIG. 1 is a block diagram of a conventional navigation apparatus. In FIG. 1, reference numerals 1, 2 and 3 designate detecting devices which include, for instance, an earth magnetism sensor, a vehicle speed sensor and a gyro sensor. The earth magnetism senses earth's magnetic field to detect the absolute direction of the vehicle, the vehicle speed sensor detects the speed of a vehicle from the speed of rotation of the wheels or the like. The gyro sensor detects the relative turning direction of a vehicle. For example, when the yaw rate is high or the tires slip, the gyro sensor is not always reliable. In such cases, the output of the earth magnetism sensor takes precedence over that of the gyro sensor.
The outputs of the detecting circuits 1, 2 and 3 are applied to an A/D (analog-to-digital) converter circuit 4, where they are converted into digital signals. The digital signals are supplied to a processor 5. The processor 5 operates upon the input data, which is two-dimensional coordinates, to detect and determine the present position of the vehicle.
In FIG. 1 reference numeral 6 designates an operating unit composed of a keyboard and switches. The operating unit 6 is operated to input predetermined instructions or commands. When the operating unit 6 applies an input signal to a control circuit 8 (inclusive of a microcomputer), the control circuit 8 causes the relevant circuits and units to operate according to the input signal, and, when necessary, activates a display unit 7 implemented with lamps and LEDs (light-emitting diodes), for example.
Upon reception of a navigation operation start instruction, the control circuit 8 causes a reproducing device, namely, a player 9, to play back a disk (CD-ROM or the like). Map data have been recorded in a digital mode on the disk. The control circuit 8 causes the player 9 to search and reproduce a map including the present position inputted by the processor 5. The player 9 outputs digital data, which is applied to a decoder 16. In the decoder 16, the digital data is decoded into data in the two-dimensional coordinates. The data thus decoded is stored in a memory 17 temporarily. The data read from the memory 17 is converted into an analog video signal, which is applied to a composing circuit 13. In response to the output signal of the circuit 13, a drive circuit 14 causes a display 15, which is preferably a CRT (cathode-ray tube) to display the map data.
In a comparator circuit 11, the output of the processor 5 is compared with that of the memory 17. The comparison result is applied to a correcting circuit 12. When the present positioned detected by the processor 5 does not coincide with a predetermined one of the data outputted by the memory means 17, the correcting circuit 12 operates to correct the present position to the data closest thereto. For instance, in the case where the present position detected by the processor 5 is off the road on the map, the present position is corrected so that it is located on the nearest road. The signal (vehicle mark) representing the present position thus corrected is applied to the composing circuit 13 where it is combined with the map data provided by the memory 17, the output of the composing circuit 13 is displayed by the display 15 with the aid of the drive circuit 14.
When the present position changes, the processor 5 obtains the travel locus form the old present position and the new present position. The travel locus thus obtained is displayed on the display 15, similar to the case of the present position.
The operator of the vehicle can obtain the vehicle's present position on the map displayed by viewing the display 15 to thus drive the vehicle to the desired destination.
In the conventional navigation apparatus where map data is recorded in a digital mode on a disk in the above-described manner, the picture displayed on the display is insufficient in resolution, color tone and number of colors, and hence it is rather difficult to view. The map displayed on the display 15 appears completely different in pattern from those to which the operator is accustomed (i.e., a map printed on paper). Therefore, it is often impossible for the operator to locate the present position quickly on the map, and at worst he may locate his vehicle in error. The resolution can of course be increased; however, a straightforward increase of the resolution suffer from the difficulty that the amount of data which must be stored is increased, and therefore the access time is increased and the capacity of the memory must be increased, making the navigation system is unavoidably high in manufacturing cost.
For instance, in the case where, similar to the NTSC television system, the display has 525 scanning lines, and each scanning line is composed of 400 dots, eight colors (3 bits) are employed, and eight tones (3 bits) are used, the data requirement for one picture is: EQU 525.times.400.times.3.times.3/8 N 236 K bytes
That is, one picture is made up of about 240 K bytes of data, the effective data transfer rate of a CD-ROM is not more than about 130 K bytes. Therefore, it takes at least two or three seconds to read the data for one picture (one map). Also, the number of maps which can be recorded on one disk is limited to about two hundred at the maximum.